Add in doco examples for how to clone a remote repo using a proxy

[davidcba1]

Hey,

I'm trying to work out how to use pygit2 to clone a remote repo using a proxy, i'm looking at some of the examples and I need to define a username/password which is fine but I can't work out how to use the proxy setting as well.

I'm referencing the following articles, but going around in circles

This one for user/pass
https://www.pygit2.org/recipes/git-clone-ssh.html

This one for remotes
https://www.pygit2.org/recipes/git-clone-mirror.html

and in the doco these bits
https://www.pygit2.org/remotes.html#pygit2.Remote.connect
https://www.pygit2.org/repository.html#pygit2.clone_repository

So this is 1 asking for guidance, but also a "recipe" for how to do this for future users.